A quick thing to note is that the amount of students who study French that also study Japanese is the same as the amount who study Japanese that also study French. Same thing.

(1) essentially repeats the information given in the problem statement, but with a discrete number of students, not a percentage. This is enough to tell us exactly how many students at the school study French (400), but not much else. Insufficient.

(2) says that 10 percent of the students at the school study both subjects. If the two groups were split evenly, it would be 10 percent of each group that study both subjects, but the problem statement gives 4 percent of those who study French instead of 10. This implies that the French group is larger. Sufficient.

B.

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